1. Field of the Invention
The present invention relates to the art of bar code scanning, and more particularly to apparatuses for measuring absolute spatial distances of bars and spaces within bar codes, and to a method for determining a precise absolute distance of the widths of bars and spaces.
2. Description of the Prior Art
In the past, apparatuses for measuring relative widths or distances of bar codes have been provided having a light source and a photodetector for detecting light reflected from a light source off of a label or sheet having a bar code imprinted thereon. Such apparatuses require either portability so that the light source and detector, together with some related circuitry can be passed over a bar code imprint, or movement of the bar code imprint past the light source and detector circuit. Such movement is designed to be made by a human holding either the bar code detecting circuitry or holding the bar code imprint. Such scanning apparatuses are used primarily for verifying the accuracy of the bar code imprint, in order to determine whether the bar code when read by standard bar code readers as, for example, grocers and retail stores will produce the correct billing and identification information in the bar code readers.
In making such a check on the bar code, apparatuses in the past have had to make certain assumptions. For example, in digital processing of the information sensed by the photodetector, it is normally assumed that the velocity of the passing of the scanner over the bar code, or vice versa as the case may be, is a constant velocity from the beginning of the bar code to the end of the bar code. Such assumptions may not be valid for relatively wide bars or wide spaces in the bar code. Moreover, most bar codes have sufficient width so that the slightest distraction by the person holding the bar code scanner or the bar code imprint will cause a variation in the velocity, and hence inaccurate readings in the readout or output of the scanning circuitry.
Moreover, such measurements necessarily are not absolute, but measure the relative distances of the width of the bars and the spaces to each other or to some standard reference. In the past, it has been necessary to have relatively large tolerances in the width of the bars and the spaces in order to accommodate the foreseeable inaccuracies in measuring such widths or distances by handheld scanning devices and photodetectors. The necessity for incorporating such tolerances within reading devices has necessarily limited the precision and the quantity of information that can be stored in bar code imprints in given widths or distances.
It has been desired for some time to have a bar code measuring apparatus that will measure the absolute spatial distances or widths or bars and spaces in bar codes without relying on relative and proportional widths of the bars and the spaces to each other. It is also desired to have bar code measuring apparatuses that can make absolute spatial measurements of the widths or distances of bars and spaces, which are portable and operable by a human holding such apparatuses. It has been desired, further, to have a bar code measuring apparatus that is capable of establishing or having established its own fixed and predetermined spatial reference distance against which the widths or distances of bars and spaces in the bar code can be absolutely and precisely measured. It is desired yet further to have a method for precisely determining the absolute spatial distance or width of bars and spaces in a bar code which does not rely on additional equipment for providing known velocities in the passing of a bar code over a scanner, or of passing a bar code measuring apparatus or scanner over a bar code.